A SiC single crystal is thermally and chemically very stable, superior in mechanical strengths, and resistant to radiation, and also has superior physical properties, such as high dielectric breakdown voltage and high thermal conductivity compared to a Si single crystal. Therefore it can achieve high power, high-frequency, high voltage resistance, high environmental resistance, etc., that conventional semiconductor materials, such as a Si single crystal and a GaAs single crystal have not been able to realize, and has been attracting interest as a next-generation semiconductor material covering a broad range, including a power device material enabling high-power regulation or energy saving, a device material for high speed large volume information communication, an in-vehicle high temperature device material, and a radiation resistant device material.
As typical growth processes for a SiC single crystal, a gas-phase process, an Acheson process, and a solution process have been heretofore known. With respect to a gas-phase process, for example, a sublimation process has a drawback in that a lattice defect and a crystal polymorph, such as a through-hole like defect referred to as a micro-pipe defect and a stacking fault are apt to appear in a grown single crystal. However, most SiC bulk single crystals have been heretofore produced by a sublimation process due to its high crystal growth speed, and some trials have been conducted to reduce defects in a grown crystal (Patent Literature 1). In an Acheson process, since silica stone and coke are used as source materials, which are heated in an electrical oven, it is not possible to obtain a high crystallinity single crystal due to impurities in the source materials.
In a solution process, melted Si or melted Si containing an alloy melt is formed in a graphite crucible, C of the graphite crucible is dissolved into the melt, and a crystalline layer of SiC is allowed to be deposited on a seed crystal substrate placed at a low temperature region, and to grow. Since, in a solution process, a crystal is grown under conditions closer to a thermal equilibrium compared to a gas-phase process, it can be expected that defects are reduced. Consequently, some production processes for a SIC single crystal based on a solution process have been recently proposed (Patent Literature 2).